Product containing an anionic cellulose derivative and its use in paper industry

ABSTRACT

A product includes a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative, as a combined preparation for simultaneous or separate use. The anionic cellulose derivative has a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65. Additionally, a paper sheet includes the product as an additive to increase the initial wet web strength and/or dry tensile strength of the paper sheet.

The present invention relates to the field of paper industry, particularly, paper making.

Paper is usually produced from pulp, which is a lignocellulosic fibrous material obtained from wood or non-wood material (e.g., cotton, bagasse, etc.). Wood pulp is separated into two main categories: either hardwood pulp or softwood pulp. Hardwood is wood from angiosperm trees (e.g., birch, eucalyptus), whereas softwood is wood from gymnosperm trees (conifers, e.g., spruce, pine). On average, softwood fibers are more than three times the length of hardwood fibers; this is why pulp obtained from softwood is called “long fiber pulp” and pulp obtained from hardwood is called “short fiber pulp”. As an increased fiber length usually provides more inter-fiber bonding, softwood pulp usually leads to products having a higher strength than products obtained from hardwood pulp.

During paper making, pulp is provided and may be refined and mixed with water to provide an aqueous pulp mixture (or pulp furnish), which can contain manufacture additives. The aqueous pulp mixture may be provided as a wet web, water is then drained from the web, which provides a wet paper sheet. The wet paper sheet is then pressed, dried, and finally rolled into large rolls.

Nowadays, industrials mainly use softwood pulp due to its higher inter-fiber bonding properties that allows running machine at a high speed and thus, increases productivity. The initial wet web strength (IWWS) is a feature describing the strength of a paper sheet before drying. When the IWWS of a sheet is increased, the machines can be run at a higher speed, thus providing a significant industrial improvement.

Therefore, there is a need to increase the IWWS of sheets comprising short fibers, in particular, sheets comprising mainly short fibers, or even only short fibers and no long fibers. Such increase will also improve the runnability of machines during papermaking.

In addition, the use of a hardwood tree such as eucalyptus is beneficial in terms of costs, since eucalyptus is a fast-growing tree that can be harvested after only 8 years.

It has now been found that using a microfibrillated cellulose composition, a starch derivative and an anionic cellulose derivative as additives during paper making makes it possible to increase the initial wet web strength, thus allowing using “short fiber pulp” without encountering the above-mentioned drawbacks.

Also, it has been found that these additives also confer advantageous properties with respect to increasing dry tensile strength.

Dry tensile strength is indicative of the strength derived, notably, from fiber strength, fiber length, and bonding. It can be used as an indication of the potential resistance to web breaking of papers such as printing papers during printing on a sheet fed press, web fed press or other web fed converting operations.

Using a microfibrillated cellulose composition, a starch derivative and an anionic cellulose derivative as additives during paper making thus allows the obtention of paper sheets having overall improved properties, in particular when used in a printing process.

The invention thus relates to a product (or a kit) comprising:

-   -   a microfibrillated cellulose composition,     -   a starch derivative, and     -   an anionic cellulose derivative having a number average         molecular weight comprised between 300000 g/mol and 800000         g/mol, and a degree of substitution comprised between 0.3 and         0.65,

as a combined preparation for simultaneous or separate use.

The product or kit according to the invention is a juxtaposition of separate but functionally interacting individual components: a microfibrillated cellulose composition, a starch derivative and a specific anionic cellulose derivative (“kit-of-parts”)

By “microfibrillated cellulose composition”, it is intended a composition comprising cellulose microfibrils or cellulose microfibril bundles that are present in the cell walls of plants (including wood). The microfibrillated cellulose composition may originate from wood or from cellulose containing biomass, for example originating from agricultural crops which may have been processed such as agricultural wastes, by-products or secondary streams of processing streams The cellulose containing agricultural biomass may originate from vegetables, fruits, grasses, buckwheat, members of the Fabeceae family, or combinations thereof.

Microfibrillated cellulose (MFC) may also be called interchangeably nanofibrillar cellulose (NFC), nanofibrillated cellulose, cellulose nanofiber, nano-scale fibrillated cellulose, microfibrillar cellulose or cellulose nanofibrils (CNF).

The microfibrils in the microfibrillated cellulose composition may have a length higher than or equal to 1 μm and a diameter comprised between 2 and 200 nm.

Preferably, the microfibril length is comprised between 1 and 200 μm, more preferably, between 10 and 100 μm, even more preferably, between 10 and 60 μm.

Preferably, the microfibril diameter is comprised between 2 and 100 m, more preferably, between 4 and 70 nm, even more preferably, between 5 and 40 nm.

Preferably, when the cellulose microfibrils form bundles, each bundle comprises between 10 and 50 microfibrils and has a diameter less than 1 μm.

It will be noted that in the context of the present application, and unless otherwise stipulated, the ranges of values indicated are understood to be inclusive.

As the microfibrillated cellulose composition may be extracted from a natural source, it may comprise other components than cellulose. Preferably, the microfibrillated cellulose composition comprises at least 30 wt % of cellulose, preferably, between 50 and 99 wt % of cellulose, more preferably, between 60 and 90 wt % of cellulose, based on the dry weight of the microfibrillated cellulose composition.

Preferably, the microfibrillated cellulose composition is not soluble in water. In a preferred embodiment, the microfibrillated cellulose of the microfibrillated cellulose composition is not chemically modified and physically modified.

By “starch derivative”, it is intended starch constituted by amylose and amylopectin that may have been chemically modified by grafting identical or different chemical compounds via their hydroxyl groups.

Advantageously, the starch derivative is derived from any suitable starch used in paper making, such as potato, rice, corn, waxy corn, wheat, barley or tapioca starch, preferably, wheat, corn or potato starch. Typically, the amylopectin content of the starch is comprised between 65 and 90 wt %, preferably between 70 and 85 wt %.

Advantageously, at least 70 wt % of the starch units of the starch derivative have a number average molecular weight higher than 20000000 g/mol, preferably, higher than 50000000 g/mol, more preferably, higher than 100000000 g/mol.

Preferably, the starch derivative is a chemically modified starch; more preferably, the starch derivative is cationic starch.

The starch may be cationized by any suitable method. Advantageously, the cationic starch is obtained by using a quaternary ammonium compound, preferably (3-acrylamidopropyl)-trimethylammonium chloride, 2,3-epoxypropyl-trimethylammonium chloride or 3-chloro-2-hydroxypropyltrimethylammonium chloride, more preferably 2,3-epoxypropyltrimethylammonium chloride.

Advantageously, the cationic starch has a degree of substitution comprised between 0.01-0.3, preferably 0.02-0.1, more preferably 0.03-0.06, where the degree of substitution indicates the number of cationic groups of the starch on average per glucose unit.

Advantageously, the cationic starch is non-degraded, which means that the starch has been modified solely by cationization, and its backbone is non-degraded and non-cross-linked.

Examples of degradation processes are, for example, oxidation and acid-thinning.

By “anionic cellulose derivative”, it is intended cellulose which is chemically modified by substitution of some hydrogens of the hydroxyl groups with carboxymethyl groups under their anionic form (i.e. some of the —OH groups are modified to —OCH₂COO⁻ groups).

The anionic cellulose derivative is different from sodium carboxymethylcellulose (CMC) due to its higher molecular weight and its lower degree of substitution, the degree of substitution indicating the number of carboxymethyl groups of the cellulose on average per glucose unit.

Indeed, CMC has a number average molecular weight typically comprised between 70000 g/mol and 100000 g/mol for uses in paper industry, and a degree of substitution which is at least 0.6, typically over 0.7 for uses in paper industry.

On the contrary, the anionic cellulose derivative has a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65.

Preferably, the anionic cellulose derivative has a number average molecular weight comprised between 400000 g/mol and 700000 g/mol, more preferably, between 450000 g/mol and 650000 g/mol, even more preferably, between 450000 g/mol and 600000 g/mol.

Preferably, the degree of substitution of the anionic cellulose derivative is comprised between 0.4 and 0.5, more preferably between 0.45 and 0.5.

In a preferred embodiment, the anionic cellulose derivative has a number average molecular weight comprised between 450000 g/mol and 600000 g/mol and a degree of substitution comprised between 0.45 and 0.5.

The number average molecular weight of the anionic cellulose derivative may be calculated using the degree of polymerization (DP) and the degree of substitution (DS) thereof determined by methods known to a person skilled in the art, and the approximative number average molecular weight of the anionic cellulose derivative can be calculated from:

DP×(162+81×DS), wherein DP is degree of polymerization and DS is degree of substitution.

The microfibrillated cellulose composition, the starch derivative and the specific anionic cellulose derivative of the product or kit according to the invention can be used or introduced simultaneously or separately, such as sequentially, in a process such as a paper making process.

Advantageously, the product according to the invention can be used in an aqueous pulp mixture together with additives which are usual in the field, as defined below. In particular, additives such as a retention system e.g., a cationic retention polymer (e.g., natural and/or synthetic cationic polymer), retention chemicals (e.g., silica sol or bentonite), etc.

The invention also relates to an admixture composition comprising:

-   -   an aqueous pulp mixture, and     -   a microfibrillated cellulose composition,     -   a starch derivative, and     -   an anionic cellulose derivative having a number average         molecular weight comprised between 300000 g/mol and 800000         g/mol, and a degree of substitution comprised between 0.3 and         0.65.

By “aqueous pulp mixture”, it is intended a mixture comprising water and pulp, preferably, a mixture consisting of water and pulp.

By “pulp”, it is meant a fibrous cellulosic material, originating from softwood, hardwood or non-wood sources, such as bamboo or kenaf or mixtures thereof. Preferably the fibrous material comprises hardwood or softwood originating fibrous material. Pulp may be cellulosic fiber material and may originate from any suitable mechanical, semi-mechanical or chemical pulping process or any of their combinations or any other suitable pulping process known as such. Such pulps may be bleached or unbleached pulps. The cellulosic fiber material may also comprise fiber material which originates from recycled board, paper or pulp. For example, cellulosic fiber material may comprise cellulosic fibers that originate from hardwood and have a length of 0.5-1.5 mm (“short fibers”) and/or softwood and have a length of 2.0-7.5 mm such as 2.5-7.5 mm (“long fibers”). Often the length of softwood fibers is in the magnitude of three times the length of hardwood fibers.

Preferably, the pulp is wood pulp, more preferably, the pulp is hardwood pulp such as eucalyptus, beech, birch, maple, willow and rose apple pulp, even more preferably, eucalyptus or birch pulp.

Advantageously, the aqueous pulp mixture comprises at least 80 wt % of short fibers, relative to the total weight of fibers. Preferably, “short fibers” are hardwood fibers (fibers from e.g., birch, eucalyptus).

The average fiber length in hardwood chemical pulp is typically 0.5 mm-1.5 mm (“short fiber”), and the average fiber length in softwood chemical pulp is typically 2.0 mm-5.0 mm (“long fiber”).

The rest of the aqueous pulp mixture comprises preferably long fibers, more preferably softwood fibers (conifers), relative to the total weight of fibers. Softwood pulp can be, for example, pine or spruce pulp.

Preferably, the aqueous pulp mixture of the admixture composition comprises at least 90 wt % of short fibers, more preferably, 100 wt % of short fibers, relative to the total weight of fibers.

Advantageously, the aqueous pulp mixture has a solid content of less than 3 wt % based on the total weight of the aqueous pulp mixture, preferably, less than 2 wt %, more preferably, less than 1 wt %, such as for example, 0.5 wt %.

All general and preferred embodiments of the microfibrillated cellulose composition, the starch derivative and/or the anionic cellulose derivative, as described above, also apply to the admixture composition.

Therefore, the microfibrillated cellulose of the microfibrillated cellulose composition is more preferably not chemically and/or physically modified, and/or the starch derivative is more preferably cationic starch, and/or the degree of substitution of the anionic cellulose derivative is comprised between 0.4 and 0.5, more preferably between 0.45 and 0.5.

Advantageously, the admixture composition according to the invention further comprises at least one additive, which can be added to the aqueous pulp mixture, simultaneously or subsequent to the microfibrillated cellulose composition, the starch derivative and the anionic cellulose derivative which are described above.

For example, a retention system such as a cationic retention polymer can be added to the aqueous pulp mixture, for example, at least one natural and/or synthetic cationic polymer.

The cationic retention polymer may be any suitable retention polymer, for example a cationic polyacrylamide (CPAM) having an average molecular weight of 4000000 to 18000000 Da, preferably 4000000-12000000 Da, more preferably 7000000-10000000 Da and/or a charge density of 0.2-2.5 meq/g, preferably 0.5-1.5 meq/g, more preferably 0.7-1.2 meq/g.

The value “average molecular weight” of the retention polymer is used to describe the magnitude of the polymer chain length. Average molecular weight values are calculated from intrinsic viscosity results measured in a known manner in 1N NaCl at 25° C. The capillary selected is appropriate for the viscosity value to be measured, and in the measurements of this application an Ubbelohde capillary viscometer with constant K=0.005228 was used. The average molecular weight is then calculated from intrinsic viscosity result in a known manner using Mark-Houwink equation [D]=K·Ma, where [D] is intrinsic viscosity, M molecular weight (g/mol), and K and a are parameters given in Polymer Handbook, Fourth Edition, Volume 2, Editors: J. Brandrup, E. H. Immergut and E. A. Grulke, John Wiley & Sons, Inc., USA, 1999.

Further, the charge density of the polymer may be determined at pH 7 and measured by titration with Mütec PCD instrument with PesNa. The absolute value herein is to be interpreted as a real number x being the non-negative value of x without regard to its sign, e.g., the absolute value of 1 is 1, and the absolute value of −1 is also 1.

Advantageously, retention chemicals such as silica particles or silica microparticles, e.g under the form of silica sol, or bentonite can be added to the aqueous pulp mixture.

The silica sol may be added to the aqueous pulp mixture in an amount of about 0.01-0.06 wt % silica/aqueous pulp mixture, such as about 0.02-0.06 wt %, or 0.03 to 0.05 wt %, based on the dry solid content of the silica sol relative to the dry solid content of the aqueous pulp mixture.

Advantageously, the amount of microfibrillated cellulose composition in the admixture composition according to the invention is comprised between 0.3 wt % and 5 wt %, based on the dry solid content of the microfibrillated cellulose composition relative to the dry solid content of the aqueous pulp mixture.

Preferably, the amount of microfibrillated cellulose composition is comprised between 0.4 wt % and 3 wt %, more preferably between 0.5 wt % and 2 wt %, such as for example 1 wt %.

Advantageously, the amount of starch derivative in the admixture composition according to the invention is comprised between 0.1 wt % and 2 wt %, based on the dry solid content of the starch derivative relative to the dry solid content of the aqueous pulp mixture.

Preferably, the amount of starch derivative is comprised between 0.3 wt % and 1.8 wt %, more preferably between 0.5 wt % and 1.5 wt %, such as for example 0.5 wt %.

Advantageously, the amount of anionic cellulose derivative in the admixture composition according to the invention is comprised between 0.05 wt % and 0.3 wt %, based on the dry solid content of the anionic cellulose derivative relative to the dry solid content of the aqueous pulp mixture.

Preferably, the amount of anionic cellulose derivative is comprised between 0.05 wt % and 0.2 wt %, such as for example 0.2 wt %.

In a preferred embodiment, the admixture composition according to the invention comprises:

-   -   between 0.3 wt % and 5 wt % of a microfibrillated cellulose         composition, based on the dry solid content of the         microfibrillated cellulose composition relative to the dry solid         content of the aqueous pulp mixture,     -   between 0.1 wt % and 2 wt % of cationic starch, based on the dry         solid content of the cationic starch relative to the dry solid         content of the aqueous pulp mixture, and     -   between 0.05 wt % and 0.3 wt % of an anionic cellulose         derivative having a molecular weight comprised between 300 000         g/mol and 800 000 g/mol, and a degree of substitution comprised         between 0.3 and 0.65, based on the dry solid content of the         anionic cellulose derivative relative to the dry solid content         of the aqueous pulp mixture.

Preferably, the microfibrillated cellulose in the microfibrillated cellulose composition is not chemically and/or physically modified.

Also, in particular, the admixture composition according to the invention may further comprise a retention system, e.g., at least one retention polymer such as a cationic retention polymer, preferably a cationic polyacrylamide as defined above, and/or at least one other retention chemicals, such as microparticles, for example, silica and/or bentonite particles. The retention system may also comprise a second retention polymer, cationic or anionic, such as in addition to the cationic retention polymer and optionally the microparticles.

The invention also relates to a process for preparing the admixture composition according to the invention, comprising:

-   -   providing an aqueous pulp mixture,     -   admixing to the aqueous pulp mixture: a microfibrillated         cellulose composition, a starch derivative, and an anionic         cellulose derivative having a number average molecular weight         comprised between 300000 g/mol and 800000 g/mol, and a degree of         substitution comprised between 0.3 and 0.65.

Preferably, the at least one cationic retention polymer and/or the at least one other retention chemical and/or additive usual in the technical field of paper making, as described above, is added to the aqueous pulp mixture.

All general and preferred embodiments of the aqueous pulp mixture, the microfibrillated cellulose composition, the starch derivative and/or the anionic cellulose derivative, as well as of the admixture composition, also apply to the process for preparing the admixture composition.

In particular, the aqueous pulp mixture advantageously has a solid content of less than 3% based on the total weight of the aqueous pulp mixture.

The microfibrillated cellulose composition, the starch derivative, and the anionic cellulose derivative can be added simultaneously or sequentially, in either order, to the aqueous pulp mixture, either to the thin or thick stock. In one embodiment of the invention, the anionic cellulose derivative and/or the microfibrillated cellulose composition can be added to the thick stock. Preferably, the anionic cellulose derivative is added to the thick stock.

In particular, thin stock typically has a solid content of less than 2 wt %, for example about 1 wt %, based on the total weight of the stock. Furthermore, thick stock typically has a solid content of about 3 to 4 wt %, based on the total weight of the stock.

In an embodiment of the invention, the anionic cellulose derivative, the starch derivative, the microfibrillated cellulose composition and the optional retention system e.g. the optional cationic polyacrylamide can be added sequentially according to this addition order.

Furthermore, the invention relates to a paper product comprising a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative having a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65.

By “paper product”, it is intended, for example, fine papers, printing paper, toilet paper, tissues or packaging materials, or else paperboard Preferably, the paper product is, for example, selected from fine papers, printing paper, toilet paper, tissues or packaging materials.

The microfibrillated cellulose composition, the starch derivative, and the anionic cellulose derivative are as described above, including the embodiments.

Preferably, the paper product according to the invention is obtained from the aqueous pulp mixture as described above. In particular, the paper product according to the invention preferably comprises 80 wt % of short fibers, more preferably, 90 wt % of short fibers, even more preferably, 100 wt % of short fibers, relative to the total weight of fibers.

The invention also relates to a process for preparing a paper product, comprising:

-   -   providing an aqueous pulp mixture,     -   admixing to the aqueous pulp mixture: a microfibrillated         cellulose composition, a starch derivative and an anionic         cellulose derivative, as described above, and optionally a         retention system such as a cationic polyacrylamide, to form an         admixture composition according to the invention, and     -   forming a wet sheet by draining the admixture composition,         wherein the anionic cellulose derivative has a number average         molecular weight comprised between 300000 g/mol and 800000         g/mol, and a degree of substitution comprised between 0.3 and         0.65.

Preferably, the process for preparing a paper product according to the invention further comprises:

-   -   pressing the wet sheet, and     -   drying the wet sheet.

According to an embodiment, in the process for preparing a paper product according to the invention, the anionic cellulose derivative is added to the aqueous pulp mixture at least 10 minutes, preferably at least 20 minutes, more preferably about 30 minutes before the wet sheet formation.

This process for preparing the paper product according to the invention encompasses all the embodiments described for the admixture composition according to the invention and all general and preferred embodiments described above for the microfibrillated cellulose composition, the starch derivative and the anionic cellulose derivative.

Advantageously, this process for preparing a paper product according to the invention provides the paper product according to the invention as described above.

The invention relates to the use of the product or kit according to the invention, as a strength additive for increasing the initial wet web strength and/or dry tensile strength of a paper sheet.

Advantageously, the product according to the invention is used to improve runability of machines during the preparation of a paper product.

The invention further relates to a product or kit comprising:

-   -   a microfibrillated cellulose composition,     -   a starch derivative, and     -   an anionic cellulose derivative having a number average         molecular weight comprised between 300000 g/mol and 800000         g/mol, and a degree of substitution comprised between 0.3 and         0.65, as defined above, in association, for joint use in a paper         making process.

By “joint use” is meant the use of a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative having a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65, as defined above, in order to obtain the desired properties of the paper product with respect to IWWS and/or dry tensile strength, the microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative having a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65, being capable of being introduced simultaneously or separately, such as sequentially, during the paper making process, preferably in the aqueous pulp mixture.

The invention is further described in the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples.

EXAMPLE 1: EVALUATION OF IWWS OF HAND SHEETS PREPARED FROM BIRCH PULP

1.1 Pulping of Birch Furnish

Birch pulp were refined with Voith Sulzer-refiner to a Schopper-Riegler (SR) value of 22, determined according to the method set forth in ISO 5267-1 Pulps—Determination of drainability—Part 1: Schopper-Riegler method. The consistency (or solid content) of the disintegrated pulp was 3 wt %. The pulp was further diluted with water prior to sheet formation to a solid content of 0.5 wt % with respect to the total weight of the aqueous pulp mixture.

1.2 Preparation of Hand Sheets

The laboratory hand sheets were prepared with dynamic sheet former (TechPap). The chemicals were added to the pulp system in the following order:

1. Anionic cellulose derivative: ECA (Nouryon); chemically modified cellulose having anionic carboxymethyl substituents with a degree of substitution comprised between 0.45 and 0.5 and a number average molecular weight of about 500 000 g/mol.

2. Cationic starch (Raisamyl)

3. Sugar beet originated microfibrillated cellulose composition (MFC) having a cellulose content of 49 wt %, based on dry solid content of the MFC, and a solid content of 18.6 wt %, based on the total weight of the MFC; the Brookfield viscosity of a 1 wt % MFC aqueous solution is 0.106 Pa·s at 100 rpm, and 0.192 Pa·s at 50 rpm (a V75 vane spindle was used for the measurement)

4. Cationic polyacrylamide (CPAM): Fennopol K3400 (Kemira Oyj)

5. Silica microparticles: Fennosil 2180 having a 6.5 wt % concentration (Kemira Oyj).

The normal delay time to add these chemicals is the following: cationic starch is added 30 s after ECA, MFC is added 60 s after ECA, CPAM is added 70 s after ECA and silica is added 80 s after ECA, the sheet formation occurring 90 s after the addition of ECA.

The sheet average grammage was 100 g/m².

After the sheet formation, the sheets were placed between plotting papers and pressed with a lab nip press under 5 bar pressure. The pressing was repeated twice after which the sheets were cut in 15 mm×150 mm cross direction (CD) and machine direction (MD) pieces. The pieces were placed into a plastic minigrip bag to avoid changes in the solid content prior the initial wet web strength (IWWS) measurements.

1.3 Measurement of the Solid Content, IWWS and Dry Tensile Strength

The solid content of the pressed sheets was measured with placing a sample into 150° C. dryer for 10 minutes and measuring the weight loss of the dried paper pieces.

Dry tensile strength was measured on dried sheets.

Dry tensile strength was measured by using method ISO 1924-3.

IWWS was measured with tensile strength measuring equipment similarly to the dry tensile strength, except that the sheets were not dried. Each test point measurement was repeated with 8 separate paper slices per machine direction and 6 per cross direction.

1.4 Results

The results for the different tested compositions are indicated in Table 1 below, wherein percentages of ECA, cationic starch, MFC, CPAM and silica are expressed as weight percentages based on the dry solid content of the component with respect to the dry solid content of the aqueous pulp mixture.

Compositions 5 and 6 are compositions according to the invention, whereas compositions 1-4 are comparative compositions. ECA was added either with normal delay time (90 seconds between addition of ECA and sheet formation) for compositions 1-5, or with long delay time (30 minutes between addition of ECA and sheet formation) for composition 6.

TABLE 1 ECA Cationic MFC CPAM Silica IWWS Solid content Dry tensile Test (%) Starch (%) (%) (%) (%) (N) (wt %) (Nm/g) 1 — — — 0.02 0.2 2.191 35.11 51.56 2 — 0.5 — 0.02 0.2 2.394 36.65 64.16 3 — 0.5 1.0 0.02 0.2 2.372 37.86 63.86 4 0.2 0.5 — 0.02 0.2 2.358 37.02 64.01 5 0.2 0.5 1.0 0.02 0.2 2.421 37.01 63.04 6 0.2 0.5 1.0 0.02 0.2 2.529 36.79 65.4

The results show that, for a similar solid content, the birch sheets obtained from the compositions 5 and 6 according to the invention have the higher IWWS, while a combination of starch with either ECA (composition 4) or MFC (composition 3) leads to sheets having an IWWS less than sheets obtained with addition of starch only (composition 2).

Furthermore, the compositions 5 and 6 according to the invention show a significant increase of the dry tensile strength with respect to the reference sheet (composition 1).

Consequently, the results show that the compositions according to the invention are able to highly increase the IWWS, as well as the dry tensile strength.

EXAMPLE 2: EVALUATION OF IWWS OF HAND SHEETS PREPARED FROM EUCALYPTUS PULP

1.1 Pulping of Eucalyptus Furnish

Eucalyptus pulp was obtained by following the method described in point 1.1 of Example 1.

1.2 Preparation of Hand Sheets

Hand sheets were obtained according to point 1.2 of Example 1, except that eucalyptus pulp was used instead of birch pulp, and a different MFC was used. This MFC is a sugar beet originated MFC having a cellulose content of 69 wt %, based on dry solid content of the MFC, and a solid content of 7.7 wt %, based on the total weight of the MFC; the Brookfield viscosity of a 1% MFC aqueous solution is 0.940 Pa·s at 100 rpm, and 1.725 Pa·s at 50 rpm (a V75 vane spindle was used for the measurement).

1.3 Measurement of the Solid Content, IWWS and Dry Tensile Strength

The solid content, the IWWS and the dry tensile strength were measured according to the procedure described in Example 1.

1.4 Results

The results for the different tested compositions are indicated in Table 2 below, wherein percentages of ECA, cationic starch, MFC, CPAM and silica are expressed as dry weight percentages with respect to the solid content of the aqueous pulp mixture.

Composition 15 is a composition according to the invention, whereas compositions 7-14 are comparative compositions.

ECA was added with normal delay time (90 seconds between addition of ECA and sheet formation) for all compositions.

TABLE 2 ECA CMC Cationic MFC CPAM Silica IWWS Solid content Dry tensile Test (%) (%) Starch (%) (%) (%) (%) (N) (wt %) (Nm/g)  7 — — — — 0.02 0.2 2.6031 35.662 46.969  8* — — — — 0.02 0.2 2.9700 35.688 48.871  9 — — 0.5 — 0.02 0.2 2.5519 37.179 57.775 10 0.2 — — — 0.02 0.2 2.7734 37.946 49.389 11 — 0.2 — — 0.02 0.2 2.6309 35.336 47.582 12 — — — 1.0 0.02 0.2 2.9509 36.176 50.199 13 — — 0.5 1.0 0.02 0.2 2.5615 36.397 60.460 14 — 0.2 0.5 1.0 0.02 0.2 2.7554 36.364 60.924 15 0.2 — 0.5 1.0 0.02 0.2 2.9045 35.662 63.798 *The pulp was obtained from a weight ratio of 90/10 eucalyptus/softwood (long fibers)

The results show that, for a similar solid content, the sheet obtained from composition 15 according to the invention (comprising a combination of MFC, starch and ECA) has an increased IWWS, as well as an increased dry tensile strength, with respect to the reference eucalyptus sheet (composition 7).

In addition, the sheet obtained from composition 15 reaches a value close to the comparative sheet made from 90/10 eucalyptus/softwood (composition 8), and has an increased dry tensile strength compared to this sheet (composition 8), resulting in better overall properties than the comparative sheet made from 90/10 eucalyptus/softwood.

On the contrary, the eucalyptus sheets obtained from any one of the comparative compositions 9, 10, 12 (comprising only one of ECA, cationic starch or MFC) do not combine both a high IWWS and a high dry tensile strength.

In addition, the improvement in terms of both IWWS and dry tensile strength is not as high when CMC is used instead of ECA (comparison of compositions 10 and 11, and of compositions 14 and 15).

The composition according to the invention allows obtaining sheets from 100% eucalyptus pulp having an IWWS close to a sheet made from 90/10 eucalyptus/softwood (good runability), but also a better dry tensile strength (better handling properties) than said sheet. 

1. A product comprising: a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative having a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65, as a combined preparation for simultaneous or separate use.
 2. The product of claim 1, wherein the microfibrillated cellulose of the microfibrillated cellulose composition is not chemically modified nor physically modified.
 3. The product of claim 1, wherein the starch derivative is a cationic starch.
 4. The product of claim 1, wherein the degree of substitution of the anionic cellulose derivative is comprised between 0.45 and 0.5.
 5. An admixture composition comprising: an aqueous pulp mixture, a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative having a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65.
 6. The admixture composition of claim 5, wherein the aqueous pulp mixture comprises at least 80 wt % of short fibers, relative to a total weight of fibers.
 7. The admixture composition of claim 5, wherein the microfibrillated cellulose of the microfibrillated cellulose composition is not chemically modified nor physically modified.
 8. The admixture composition of claim 5, wherein the starch derivative is a cationic starch.
 9. The admixture composition of claim 5, wherein the degree of substitution of the anionic cellulose derivative is comprised between 0.45 and 0.5.
 10. The admixture composition of claim 5, further comprising a retention system.
 11. The admixture composition of claim 10, wherein the retention system comprises at least one cationic polyacrylamide.
 12. The admixture composition of claim 5, wherein an amount of microfibrillated cellulose composition is comprised between 0.3 wt % and 5 wt %, based on a dry solid content of the microfibrillated cellulose composition relative to a dry solid content of the aqueous pulp mixture.
 13. The admixture composition of claim 5, wherein an amount of starch derivative is comprised between 0.1 wt % and 2 wt %, based on a dry solid content of the starch derivative relative to a dry solid content of the aqueous pulp mixture.
 14. The admixture composition of claim 5, wherein an amount of anionic cellulose derivative is comprised between 0.05 wt % and 0.3 wt %, based on a dry solid content of the anionic cellulose derivative relative to a dry solid content of the aqueous pulp mixture.
 15. A method for preparing the admixture composition of claim 5, comprising: providing the aqueous pulp mixture, and admixing to the aqueous pulp mixture, the microfibrillated cellulose composition, the starch derivative, and the anionic cellulose derivative, and.
 16. The method of claim 15, wherein the aqueous pulp mixture has a solid content of less than 3% of a total solids content in the aqueous pulp mixture.
 17. The method of claim 15, wherein the retention system of the admixture composition comprises at least one of cationic polyacrylamide and silica.
 18. A method for preparing a paper product, comprising: providing an aqueous pulp mixture, admixing to the aqueous pulp mixture, a microfibrillated cellulose composition, a starch derivative and an anionic cellulose derivative, to form the admixture composition of claim 5, and forming a wet sheet by draining the admixture composition, and.
 19. The method of claim 18, wherein the anionic cellulose derivative is added to the aqueous pulp mixture at least 10 minutes before a wet sheet formation.
 20. A paper product comprising a microfibrillated cellulose composition, a starch derivative, and an anionic cellulose derivative having a number average molecular weight comprised between 300000 g/mol and 800000 g/mol, and a degree of substitution comprised between 0.3 and 0.65.
 21. A paper sheet comprising the product of claim 1, as an additive to increase at least one of an initial wet web strength and a dry tensile strength of the paper sheet.
 22. The method of claim 15, further comprising admixing a retention system.
 23. The method of claim 16, wherein the aqueous pulp mixture has a solid content of less than 3% of a total solids content in the aqueous pulp mixture.
 24. The method of claim 20, further comprising admixing a retention system to form the admixture composition. 